[PATCH] color-words: make regex configurable via attributes

[Thomas Rast <trast@student.ethz.ch>]

Make the --color-words splitting regular expression configurable via
the diff driver's 'wordregex' attribute.  The user can then set the
driver on a file in .gitattributes.  If a regex is given on the
command line, it overrides the driver's setting.

We also provide built-in regexes for the languages that already had
funcname patterns, and add an appropriate diff driver entry for C/++.
(The patterns are designed to run UTF-8 sequences into a single chunk
to make sure they remain readable.)

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
---

This is the old 3/4 combined with a test similar to the one it had in
the old 4/4, built on top of Dscho's take 3.  I researched the
operators for each language, but the identifier and number formats may
be off in some cases.


 Documentation/diff-options.txt  |    3 +
 Documentation/gitattributes.txt |   21 ++++++++++
 diff.c                          |   10 +++++
 t/t4034-diff-words.sh           |   40 ++++++++++++++++++++
 userdiff.c                      |   78 +++++++++++++++++++++++++++++++-------
 userdiff.h                      |    1 +
 6 files changed, 138 insertions(+), 15 deletions(-)

diff --git a/Documentation/diff-options.txt b/Documentation/diff-options.txt
index 2c1fa4b..ef0e2f5 100644
--- a/Documentation/diff-options.txt
+++ b/Documentation/diff-options.txt
@@ -97,6 +97,9 @@ endif::git-format-patch[]
 Optionally, you can pass a regular expression that tells Git what the
 words are that you are looking for; The default is to interpret any
 stretch of non-whitespace as a word.
+The regex can also be set via a diff driver, see
+linkgit:gitattributes[1]; giving it explicitly overrides any diff
+driver setting.
 
 --no-renames::
 	Turn off rename detection, even when the configuration
diff --git a/Documentation/gitattributes.txt b/Documentation/gitattributes.txt
index 8af22ec..17707ba 100644
--- a/Documentation/gitattributes.txt
+++ b/Documentation/gitattributes.txt
@@ -317,6 +317,8 @@ patterns are available:
 
 - `bibtex` suitable for files with BibTeX coded references.
 
+- `cpp` suitable for source code in the C and C++ languages.
+
 - `html` suitable for HTML/XHTML documents.
 
 - `java` suitable for source code in the Java language.
@@ -334,6 +336,25 @@ patterns are available:
 - `tex` suitable for source code for LaTeX documents.
 
 
+Customizing word diff
+^^^^^^^^^^^^^^^^^^^^^
+
+You can customize the rules that `git diff --color-words` uses to
+split words in a line, by specifying an appropriate regular expression
+in the "diff.*.wordregex" configuration variable.  For example, in TeX
+a backslash followed by a sequence of letters forms a command, but
+several such commands can be run together without intervening
+whitespace.  To separate them, use a regular expression such as
+
+------------------------
+[diff "tex"]
+	wordregex = "\\\\[a-zA-Z]+|[{}]|\\\\.|[^\\{}[:space:]]+"
+------------------------
+
+A built-in pattern is provided for all languages listed in the last
+section.
+
+
 Performing text diffs of binary files
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/diff.c b/diff.c
index eb67431..08bdc86 100644
--- a/diff.c
+++ b/diff.c
@@ -1372,6 +1372,12 @@ int diff_filespec_is_binary(struct diff_filespec *one)
 	return one->driver->funcname.pattern ? &one->driver->funcname : NULL;
 }
 
+static const char *userdiff_word_regex(struct diff_filespec *one)
+{
+	diff_filespec_load_driver(one);
+	return one->driver->word_regex;
+}
+
 void diff_set_mnemonic_prefix(struct diff_options *options, const char *a, const char *b)
 {
 	if (!options->a_prefix)
@@ -1532,6 +1538,10 @@ static void builtin_diff(const char *name_a,
 			ecbdata.diff_words =
 				xcalloc(1, sizeof(struct diff_words_data));
 			ecbdata.diff_words->file = o->file;
+			if (!o->word_regex)
+				o->word_regex = userdiff_word_regex(one);
+			if (!o->word_regex)
+				o->word_regex = userdiff_word_regex(two);
 			if (o->word_regex) {
 				ecbdata.diff_words->word_regex = (regex_t *)
 					xmalloc(sizeof(regex_t));
diff --git a/t/t4034-diff-words.sh b/t/t4034-diff-words.sh
index 0ed7e53..d6731d1 100755
--- a/t/t4034-diff-words.sh
+++ b/t/t4034-diff-words.sh
@@ -83,4 +83,44 @@ test_expect_success 'word diff with a regular expression' '
 
 '
 
+cat > expect-by-chars <<\EOF
+<WHITE>diff --git a/pre b/post<RESET>
+<WHITE>index 330b04f..5ed8eff 100644<RESET>
+<WHITE>--- a/pre<RESET>
+<WHITE>+++ b/post<RESET>
+<BROWN>@@ -1,3 +1,7 @@<RESET>
+<RED>h(4)<RESET><GREEN>h(4),hh[44]<RESET>
+<RESET>
+a = b + c<RESET>
+
+<GREEN>aa = a<RESET>
+
+<GREEN>aeff = aeff * ( aaa )<RESET>
+EOF
+
+test_expect_success 'set a diff driver' '
+	git config diff.testdriver.wordregex "[^[:space:]]" &&
+	cat <<EOF > .gitattributes
+test_* diff=testdriver
+EOF
+'
+
+test_expect_success 'use default supplied by driver' '
+
+	test_must_fail git diff --no-index --color-words \
+		pre post > output &&
+	decrypt_color < output > output.decrypted &&
+	test_cmp expect-by-chars output.decrypted
+
+'
+
+test_expect_success 'option overrides default' '
+
+	test_must_fail git diff --no-index --color-words="[a-z]+" \
+		pre post > output &&
+	decrypt_color < output > output.decrypted &&
+	test_cmp expect output.decrypted
+
+'
+
 test_done
diff --git a/userdiff.c b/userdiff.c
index 3681062..79f9cb9 100644
--- a/userdiff.c
+++ b/userdiff.c
@@ -6,14 +6,20 @@
 static int ndrivers;
 static int drivers_alloc;
 
-#define FUNCNAME(name, pattern) \
-	{ name, NULL, -1, { pattern, REG_EXTENDED } }
+#define PATTERNS(name, pattern, wordregex)			\
+	{ name, NULL, -1, { pattern, REG_EXTENDED }, NULL, wordregex }
 static struct userdiff_driver builtin_drivers[] = {
-FUNCNAME("html", "^[ \t]*(<[Hh][1-6][ \t].*>.*)$"),
-FUNCNAME("java",
+PATTERNS("html", "^[ \t]*(<[Hh][1-6][ \t].*>.*)$",
+	 "[^<>= \t]+|[^[:space:]]|[\x80-\xff]+"),
+PATTERNS("java",
 	 "!^[ \t]*(catch|do|for|if|instanceof|new|return|switch|throw|while)\n"
-	 "^[ \t]*(([ \t]*[A-Za-z_][A-Za-z_0-9]*){2,}[ \t]*\\([^;]*)$"),
-FUNCNAME("objc",
+	 "^[ \t]*(([ \t]*[A-Za-z_][A-Za-z_0-9]*){2,}[ \t]*\\([^;]*)$",
+	 "[a-zA-Z_][a-zA-Z0-9_]*"
+	 "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lL]?"
+	 "|[-+*/<>%&^|=!]="
+	 "|--|\\+\\+|<<=?|>>>?=?|&&|\\|\\|"
+	 "|[^[:space:]]|[\x80-\xff]+"),
+PATTERNS("objc",
 	 /* Negate C statements that can look like functions */
 	 "!^[ \t]*(do|for|if|else|return|switch|while)\n"
 	 /* Objective-C methods */
@@ -21,20 +27,60 @@
 	 /* C functions */
 	 "^[ \t]*(([ \t]*[A-Za-z_][A-Za-z_0-9]*){2,}[ \t]*\\([^;]*)$\n"
 	 /* Objective-C class/protocol definitions */
-	 "^(@(implementation|interface|protocol)[ \t].*)$"),
-FUNCNAME("pascal",
+	 "^(@(implementation|interface|protocol)[ \t].*)$",
+	 /* -- */
+	 "[a-zA-Z_][a-zA-Z0-9_]*"
+	 "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lL]?"
+	 "|[-+*/<>%&^|=!]=|--|\\+\\+|<<=?|>>=?|&&|\\|\\||::|->"
+	 "|[^[:space:]]|[\x80-\xff]+"),
+PATTERNS("pascal",
 	 "^((procedure|function|constructor|destructor|interface|"
 		"implementation|initialization|finalization)[ \t]*.*)$"
 	 "\n"
-	 "^(.*=[ \t]*(class|record).*)$"),
-FUNCNAME("php", "^[\t ]*((function|class).*)"),
-FUNCNAME("python", "^[ \t]*((class|def)[ \t].*)$"),
-FUNCNAME("ruby", "^[ \t]*((class|module|def)[ \t].*)$"),
-FUNCNAME("bibtex", "(@[a-zA-Z]{1,}[ \t]*\\{{0,1}[ \t]*[^ \t\"@',\\#}{~%]*).*$"),
-FUNCNAME("tex", "^(\\\\((sub)*section|chapter|part)\\*{0,1}\\{.*)$"),
+	 "^(.*=[ \t]*(class|record).*)$",
+	 /* -- */
+	 "[a-zA-Z_][a-zA-Z0-9_]*"
+	 "|[-+0-9.e]+|0[xXbB]?[0-9a-fA-F]+"
+	 "|<>|<=|>=|:=|\\.\\."
+	 "|[^[:space:]]|[\x80-\xff]+"),
+PATTERNS("php", "^[\t ]*((function|class).*)",
+	 /* -- */
+	 "[a-zA-Z_][a-zA-Z0-9_]*"
+	 "|[-+0-9.e]+|0[xXbB]?[0-9a-fA-F]+"
+	 "|[-+*/<>%&^|=!.]=|--|\\+\\+|<<=?|>>=?|===|&&|\\|\\||::|->"
+	 "|[^[:space:]]|[\x80-\xff]+"),
+PATTERNS("python", "^[ \t]*((class|def)[ \t].*)$",
+	 /* -- */
+	 "[a-zA-Z_][a-zA-Z0-9_]*"
+	 "|[-+0-9.e]+[jJlL]?|0[xX]?[0-9a-fA-F]+[lL]?"
+	 "|[-+*/<>%&^|=!]=|//=?|<<=?|>>=?|\\*\\*=?"
+	 "|[^[:space:]|[\x80-\xff]+"),
+	 /* -- */
+PATTERNS("ruby", "^[ \t]*((class|module|def)[ \t].*)$",
+	 /* -- */
+	 "(@|@@|\\$)?[a-zA-Z_][a-zA-Z0-9_]*"
+	 "|[-+0-9.e]+|0[xXbB]?[0-9a-fA-F]+|\\?(\\\\C-)?(\\\\M-)?."
+	 "|//=?|[-+*/<>%&^|=!]=|<<=?|>>=?|===|\\.{1,3}|::|[!=]~"
+	 "|[^[:space:]|[\x80-\xff]+"),
+PATTERNS("bibtex", "(@[a-zA-Z]{1,}[ \t]*\\{{0,1}[ \t]*[^ \t\"@',\\#}{~%]*).*$",
+	 "[={}\"]|[^={}\" \t]+"),
+PATTERNS("tex", "^(\\\\((sub)*section|chapter|part)\\*{0,1}\\{.*)$",
+	 "\\\\[a-zA-Z@]+|[{}]|\\\\.|[^\\{} \t]+"),
+PATTERNS("cpp",
+	 /* Jump targets or access declarations */
+	 "!^[ \t]*[A-Za-z_][A-Za-z_0-9]*:.*$\n"
+	 /* C functions at top level */
+	 "^([A-Za-z_][A-Za-z_0-9]*([ \t]+[A-Za-z_][A-Za-z_0-9]*){1,}[ \t]*\\([^;]*)$\n"
+	 /* compound type at top level */
+	 "^((struct|class|enum)[^;]*)$",
+	 /* -- */
+	 "[a-zA-Z_][a-zA-Z0-9_]*"
+	 "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lL]?"
+	 "|[-+*/<>%&^|=!]=|--|\\+\\+|<<=?|>>=?|&&|\\|\\||::|->"
+	 "|[^[:space:]]|[\x80-\xff]+"),
 { "default", NULL, -1, { NULL, 0 } },
 };
-#undef FUNCNAME
+#undef PATTERNS
 
 static struct userdiff_driver driver_true = {
 	"diff=true",
@@ -134,6 +180,8 @@ int userdiff_config(const char *k, const char *v)
 		return parse_string(&drv->external, k, v);
 	if ((drv = parse_driver(k, v, "textconv")))
 		return parse_string(&drv->textconv, k, v);
+	if ((drv = parse_driver(k, v, "wordregex")))
+		return parse_string(&drv->word_regex, k, v);
 
 	return 0;
 }
diff --git a/userdiff.h b/userdiff.h
index ba29457..2aab13e 100644
--- a/userdiff.h
+++ b/userdiff.h
@@ -12,6 +12,7 @@ struct userdiff_driver {
 	int binary;
 	struct userdiff_funcname funcname;
 	const char *textconv;
+	const char *word_regex;
 };
 
 int userdiff_config(const char *k, const char *v);
-- 
1.6.1.140.ge720e.dirty